A so-called separate type air conditioning apparatus in which an indoor unit and an outdoor unit are connected to each other via a refrigerant pipe (crossover pipe) is known. When performing a heating operation with this type of air conditioner, an indoor heat exchanger mounted on the indoor unit has a relatively high temperature, and an outdoor heat exchanger mounted on the outdoor unit has a relatively low temperature. When the outside air temperature is low, the temperature of the outdoor heat exchanger becomes 0° C. or less. When the humidity around the outdoor heat exchanger is high to a certain extent, moisture in the outside air becomes frost and adheres to the outdoor heat exchanger.
Therefore, when the heating operation is continued even after adherence of frost, there arises a problem in which frost increases, the heat exchange capacity of the outdoor heat exchanger is degraded, and the heating capacity of the air conditioning apparatus drops.
In order to prevent heating capacity degradation, when it can be presumed that the frost adhering to the outdoor heat exchanger has increased to a certain extent, a controller of the air conditioning apparatus executes an operation (a defrosting operation) for melting the adhered frost.
When the outside air temperature is extremely low, for example, −20° C. or less, humidity is low and it is difficult for frost to adhere to the outdoor heat exchanger. Even in this case, since the temperature of the outdoor heat exchanger is low, the defrosting operation is performed. Under such conditions, when the defrosting operation is performed for a long period of time, it is conceivable that problems may occur in the air conditioning apparatus.